1. Field of the Invention
The present invention relates to a transmission/reception apparatus suitable for CDMA (Code Division Multiple Access) using the multiple access scheme, and particularly to the transmission output control of the CDMA-based transmission/reception apparatus for the mobile radio communication equipment.
2. Description of the Related Art
As a transmission scheme of mobile radio communication, attention is paid recently to the spread-spectrum CDMA system which is superior in the efficiency of use of frequencies. This system is already put into practice in some fields, and it is a powerful candidate of the next-generation mobile communication system (FPLMTS: Future Public Land Mobile Telecommunication System) for the radio communication between a base station and multiple local stations.
The CDMA is designed to spread the radio wave of each station based on an unique high-speed code. Specifically, at a same time point and in a same frequency band, the sending station sends signals based on different spread codes on individual communication channels, and each receiving station retrieves only information signals on the communication channel to that station based on the spread codes assigned to it.
Other multiple access schemes include the TDMA (Time Division Multiple Access) system which transmits multiple input channel signals on a time-slice basis, and the FDMA (Frequency Division Multiple Access) system which transmits multiple input channel signals simultaneously and separately by assigning different carrier frequencies.
Among these multiple access schemes, the CDMA system which bases the resource on electric power is required of wide-range continuous control of transmission output (specifically, 80 dB for local stations) for the sake of efficient transmission. Namely, local stations are required to control their transmission outputs so that all signal levels are equal at the reception by the base station.
FIG. 22 is a block diagram showing the arrangement of a typical CDMA terminal equipment. The CDMA terminal 70 includes a codec 41, a vocoder 42, a microprocessor (MPU) 43, an encoder/decoder 44A, an interleaver/deinterleaver 44B, a spreader/modulator 45, a transmitter/receiver 46, an antenna 47, and a despreader/demodulator 48.
The codec 41 converts an analog audio signal entered to the terminal into digital data, i.e., code conversion, and the vocoder 42 determines the capacity (rate) of the input signal, i.e., in sending mode, it determines the capacity of digital audio data provided by the codec 41 and sends the result to the microprocessor 43 which will be explained shortly, and in receiving mode, it processes audio data based on the capacity provided by the microprocessor 43 and delivers the resulting audio signal as the output of the terminal.
The microprocessor (MPU) 43 sets and releases a call, and the encoder/decoder 44A encodes and decodes data and, particularly at decoding, it releases data (symbols) provided by the interleaver/deinterleaver 44B as reception data.
The interleaver/deinterleaver 44B consists of an interleaver section which functions to rearrange the sequence of signal and recover defective information based on time-shuffling thereby to improve the signal quality on the transmission path, and a deinterleaver section which functions to restore the original sequence of signal by rearranging the output (symbols) from the despreader/demodulator 48 which will be explained shortly based on a prescribed time reference (timing). The spreader/modulator 45 spreads and modulates the encoded transmission data.
The transmitter/receiver 46 implements the process for sending and receiving information to/from the base station (not shown) through the antenna 47 which will be explained shortly, and it consists of a transmitter section 46A, a DUP 46B, and a receiver section 46C.
The transmitter section 46A implements the frequency amplifying process for the output of the spreader/modulator 45 based on the transmission gain control signal provided by the despreader/demodulator 48, which will be explained shortly, for the transmission to the base station. The DUP 46B implements the branching process for directing the output of the transmitter section 46A as a transmission output to the antenna 47, and directing the radio wave introduced by the antenna 47 as a reception input to the receiver section 46C.
The receiver section 46C implements the amplifying process for the radio wave from the base station. The antenna 47 receives the radio wave which is transmitted by the base station over the radio communication path (not shown), and transmits the signal produced by the terminal in the form of radio wave. The despreader/demodulator 48 implements the demodulation process thereby to convert the spread-encoded data back to the original data, and produces the transmission gain control signal for the transmitter section 46A based on the information from the based station.
At signal transmission to the base station by the CDMA terminal 70 arranged as described above, the codec 41 digitizes the audio signal into digital data and the vocoder 42 determines the capacity (rate) of the digital audio data. The microprocessor 43 sets a call, the encoder/decoder 44A encodes the audio data, and the interleaver section of the interleaver/deinterleaver 44B rearranges the sequence of signal.
The spreader/modulator 45 implements the modulation and spreading processes for the output of the interleaver/deinterleaver 44B, and the transmitter section 46A implements the frequency amplifying process for the transmission to the base station based on the transmission gain control signal provided by the despreader/demodulator 48. The DUP 46B directs the resulting transmission output in the form of a radio wave to the antenna 47 for transmission.
At signal reception from the base station, the receiver section 46C receives the radio wave from the antenna 47 by way of the DUP 46B and amplifies the reception signal, the despreader/demodulator 48 implements the demodulation and despreading processes, and the deinterleaver section of the interleaver/deinterleaver 44B restores the original sequence of signal. The encoder/decoder 44A decodes the reception signal, and the microprocessor 43 controls the signal and extracts audio data and display/control data from the reception data. The vocoder 42 processes the audio data depending on the capacity of delivery, and the codec 41 converts the audio data back to the analog audio signal to be delivered as the output of the CDMA terminal 70.
FIG. 23 is a block diagram showing the arrangement of a typical transmitter/receiver. The transmitter/receiver 50 consists of a transmitter section 50A including a gain amplifier 20, power amplifier 21, transmission monitor signal extractor 22, and transmission filter 23, a receiver section 50B including a reception filter 28 and low-noise amplifier 29, a circulator 26, and an antenna 27. The transmission monitor signal extractor 22 has its part of output fed back to the gain amplifier 20 by way of a detection circuit 24 and controller 25.
The antenna 27 transmits and receives signals to/from other radio communication equipment over the radio communication path (not shown), and the circulator 26 is rotating to direct the transmission output from the transmitter section 50A to the antenna 27 and direct the reception input from the antenna 27 to the receiver section 50B.
The gain amplifier 200 amplifies a gain of the transmission signal by being controlled by the controller 25 which will be explained shortly, the power amplifier (PA) 21 amplifies the output of the gain amplifier 20, and the transmission monitor signal extractor 22 extracts the transmission monitor signal from the output of the power amplifier 21.
The transmission filter 23 renders the band confinment for the output of the transmission monitor signal extractor 22, and the band-confined transmission output is directed by the circulator 26 to the antenna 27 for transmission.
The detection circuit 24 implements the detection for the transmission monitor signal extracted by the transmission monitor signal extractor 22, and the controller 25 compares the resulting DC signal of the detection circuit 24 with a prescribed reference level and controls the gain of the gain amplifier 20 so that the amplified output is within a certain range. Based on the feedback of the extracted transmission monitor signal to the gain amplifier 20, the transmission output on the antenna 27 has a constant amplitude.
The reception filter 28 renders the band confinment for the reception input provided by the antenna 27 through the circulator 26, and the low-noise amplifier 29 amplifies the reception signal released by the reception filter 28.
At signal transmission by the transmitter/receiver 50 arranged as shown in FIG. 23, the transmission signal is amplified by the gain amplifier 20, with its output being further amplified by the power amplifier 21. The transmission monitor signal extractor 22 extracts from the amplified transmission signal the transmission monitor signal, which is subjected to detection by the detection circuit 24, and the controller 25 controls the amplification gain so that the amplitude of transmission signal is within a certain range. The transmission filter 23 renders the band confinment for the transmission signal, and the resulting transmission output is directed by the circulator 26 to the antenna 27 for transmission.
At signal reception, the antenna 27 receives the radio wave signal sent over the radio communication path, the reception input is directed by the circulator 26 to the reception filter 28, by which the signal is rendered the band confinment, and the low-noise amplifier 29 amplifies the resulting reception signal.
However, the detection circuit 24 of the transmitter/receiver 50 has a range of detection of 20 dB at most in general. Although this detection range is deemed sufficient for the case of the fixed transmission output power and the case of the switching of transmission output power, the circuit will suffer the deficiency when it is intended to compensate the shadowing (interruption of radio wave by a building, etc.) and multi-path-phasing (interference of radio wave with reflected radio waves) besides the variation of communication distance in mobile communication. Particularly, in the case of CDMA in which the transmission output is a resource shared among stations, a control range as wide as 80 dB is required, and this circuit is not capable of coping with the above-mentioned various radio wave disturbances.
Moreover, because of a limited output of the transmitter section 50A, what will be in question at the expansion of control range of transmission output is the lower side of the detection level. The decrease of signal level on the input of the detection circuit 24 causes the detection voltage to fall and the transmission monitor signal to be hidden in the noise, resulting in the failure of detection.